The invention relates to a circuit arrangement for driving with a phototransistor at least one thyristor connected to an alternating voltage.
Such a circuit arrangement has been described, for example, in "Siemens Components", 20 (1982), No. 3, pages 83 ff., particularly FIG. 2, all incorporated herein by reference. Given this circuit arrangement, the phototransistor controls the thyristor via an auxiliary transistor, whereby the collector-emitter path of the auxiliary transistor is parallel to the gate-collector path of the thyristor. The collector-emitter path of the phototransistor is connected via resistors to an alternating voltage proportional to the line voltage. In order to prevent an activation of the unilluminated phototransistor at rising voltage edges (dv/dt load), an RC series connection is connected parallel to the circuit arrangement at the output side. This simultaneously serves for compensation of phase changes produced by inductive loads. 100 Ohms is proposed, for example, as a resistance and 0.1 .mu.F as a capacitance. This means that a quiescent current on the order of a few mA can flow in the idle condition, i.e. given a switched off thyristor. Furthermore, such an RC wiring is poorly suited for integration given the specified dimensions.